I'm not aware that putting in a free demo (aside from the webgl /browser version) would work along with a paid content. We need to explore it further. On the upside, Steam keys do came along with an itch.io purchase of the game. Our version on Steam (particularly the BETA branch) had far more content compared to the version which usually gets updated a week (or so) after our update on Steam.
Did you know steam keys for lewd games work in Germany? You just can't see the store or buy it there, but activating a Steam key can bypass this. We do have players from Germany actively participating on our Discord server. :)
Have a look at Innocent Witches (https://sad-crab.itch.io/innocent-witches). They offer an outdated version for free alongside their latest version for 10$ or more.
Replace the outdated version with your demo and you are good.
I am for sure considering buying this, but I have to finish Paradise Lost before :-P
You can't find or buy the game in the German store, but activating the key is not an issue. That's what I did with Paradise Lust. I was very happy to see that you also get a Steam key when you buy the game here and wish more developers would handle it like this. The censorship on the German Steam store really is a pain in the ass.
@sonkhawk You can hide the game in your library, or simply create a second Steam account to be safe.